Part of a novel research project serving as BSc Zoology dissertation, produced only with the observational aid and expertise of Dr. David Crosse, Dr. Nicole Goodey, Prof. Michael Cant, Daniel Blumgart, and Ignatius W. van Rooyen.
P. occidentis Phylogeny
P. occidentis is a primitive (lower) termite species (Oder: Dictyoptera; Family: Kalotermitidae). Termites share a common ancestor from the cockroach family (Cryptocercidae) and can be thought of as a specialised form of cockroach (Eggleton 2011). After decades of unclear hypotheses and poor taxon sampling, 7 majour termite clades (Families) have been decided upon as illustrated in the diagram on the right.
P. occidentis Natural Habitat
The ecological niche that P. occidentis fills in the North American Sonoran Desert to which they are endemic, is that of decomposers. They can commonly be found nesting in dead Arizonon Cercidium trees.
What little water they obtain comes from moisture found in their food source, rare rain storms and dew fall. They depend on the protection from extreme desert weather conditions that their nest, usually enclosed in a dead tree stem and branches, provides.
In September 2011, Prof. Michael Cant and Nicole Goodey extracted P. occidentis colonies from their natural habitat, near Tucson, Arizona for use in research. The colonies were re-established under controlled lab conditions at the Center for Ecology and Conservation, Cornwall.
I was introduced to this highly cooperative primitive termite species in January 2012, when I started working as a lab intern. Joined later by Dr. David Crosse, we began to refine laboratory techniques, starting work on angles of study based on previous work involving primitive eusocial insect species, and theories of cooperative animal behaviour and evolution.
P. occidentis Physiology
P. occidentis is soft-bodied. Workers lack pigmentation while Reproductives and Soldiers are usually an auburn brown colour. These are hemimetabolistic insects meaning they undergo stages of development (metamorphosis) without a pupal stage, but molting between developmental stages to grow to maturity.
Cuticular Hydrocarbons (CHCs) found on the cuticle of insects are often cited as being particularly important for recognition cues in social insects however this is still a controversial theory.
Correlation studies have shown a wide variation in the CHC profiles between individuals from different colonies, and over time. These variations in CHC’s between individuals may affect costly social behaviour of insects in a way which can be recorded and used to shed light on the mechanisms of social evolution.
P. occidentis Colony Structure
P. occidentis colony life is a complex social system. The colony consists of different termites each of which specialises in a different role.
Pseudergates (sometimes called ‘workers’) lack pigmentation, are soft bodied and have no weaponry, although some may have wing buds at certain stages. Pseudergates grow in size, molting into different stages. They are mainly observed feeding and cleaning the colony, responsible for caring for eggs, the reproductives and soldiers, as well as building the nest.
Pseudergates also care for each other via interactions called trophalaxis and allogrooming. It is thought that they may also molt into soldiers and have been observed in the process of molting into neotenic reproductives in the event of the death of the original reproductuves. Little is known about the mechanisms of determing whether an individual remains a pseudergate, or develops into a solider or reproductive, at a certain point in time. However, it is thought that there may be a connection between environmental conditions, the current number of soldiers or reproductives present, the needs of the colony and whether or not new soldiers or neotenic reproductives are observed to appear.
The majority of the colony is made up of pseudergates at various stages of molt. Some grow wings when food is scarece in preparation for flying away to find a new food source and to start a new colony elsewhere. However, this transformation is reversible and if the food souce is replenished somehow, they lose their wing buds. Little is understood about how these termites determine the size of the food source and the amount of nutrition available at any point in time, or how they know the size of the colony itself.
Soldiers are dark brown in colour, armoured, have very large heads equiped with pincers and exhibit agressive behaviour more often than other members of the colony. There are relatively few soldiers in the colony and they are responsible for nest defence.
P. occidentis nests are sometimes at risk of invasion by a rival colony in search of a new source of food, or interested in merging colonies which involves destroying a colony’s current reporductives. Neither situation would be beneficial for the invaded colony as sharing their rare food source with a rival colony threatens their survival. They may also be genetically unrelated to the invading reproductives which means there would be a break down in the altruistic functions of the colony.
In the event of such colony invasion, soldiers may use their large heads to block the tunnels of the nest and their pincers to attack invaders. In this species, the pincers are nore particularly effective and P. occidentis seem to exhibit much lower levels of aggression than many other termite species.
Reproductives are larger than pseudergats but less bulky than soldiers. The older the reproductive, the darker its brown pigmentation and they also posess harder bodies than psuedergates but that are less armoured than soldiers. Each colony has a king and queen whose sole purpose it is to reproduce. Reproductives are less active than other colony members and are usually found together, surrounded by a dense gathering of pseudergates, constantly grooming and feeding their king and queen.
P. occidentis are hemimetabolistic insects, hatching from eggs as nymphs. They appear to be able to molt through nymphal stages, some eventually ending up as fully reproductive and others soldiers. The majority of individuals in the colony, though molting and growing in size, or even growing wing buds, reach neither the reproductive or soldier stage.
It is very important for the survival and efficient function of the colony that individuals of a colony at different stages can recognise each other as being both different, with different functions within the colony, as well as relatives from the same colony, and therefore entitled to the same colony resources and services.
I have observed that when a P. occidentis individual from one colony is introduced to members of a different colony, it is ignored. In other termite species, aggression between the colony members and the unrelated individual may be observed, but even though a non-aggressive approach to a stranger might seem counter productive for the security of the colony, it may work to prevent the occurrence of free riders from other colonies taking advantage of the social and resource benefits of a colony as previous studies suggest that social interaction is essential for the survival of individuals from primitive termite colonies.
Little is known about the mechanisms through which P. occidentis individuals distinguish between relative and non-relative individuals. Inhabiting tree stumps and branches means that termites live in total darkness most of the time and so do not have well developed eyesight, but rather seem to be able to detect changes in lighting. CHC detection or the use of gut symbionts as ways of sharing common markers and recognising each other have been suggested and researched.
In a very dry environment, where temperature extremes are not uncommon and essential resoures are hard to come by, the colony works together to grow and produce many members that all share 50% of their genes with each other as well as with their kign and queen. During this process, they pay a service to the ecosystem by re-working dead plant matter and in doing so, replenish the environment with essential nutrients for it’s continues existence and development.
P. occidentis Behaviour
Common characteristics are found in species that have developed sociality and eusociality:
1. Mating Systems: inbreeding with periodic out-crossing (for reduction of inbreeding costs) leads to high relatedness within a colony.
2. Parental Care: (at least to some extent) allows for overlapping generations within a related social group.
3. Helper evolution: due to high adult mortality, long periods of offspring dependence or delayed age of reproduction.
4. ‘Fortress Defenders’: primitive (lower) termites often live inside their food source.
5. Other factors: Mutualistic interactions and restricted dispersal can also foster the evolution of sociality.
P. occidentis are ‘fortress defenders’:
Three conditions are needed to explain the occurrence of eusociality in Fortress Defenders:
Recognition cues in social insects are thought to be chemical, with hydrocarbons found on the cuticle of insects often cited as being particularly important. According to previous work, CHC composition may change over time and between colonies and individuals.
Because termite colony members may have naturally individual profiles, a constant hydrocarbon transfer may be needed to maintain a similar overall colony profile [Boulay et al. 2000, Campoutus fellah colony integration: worker individuality necessitates frequent hydrocarbon exchanges. Animal Behaviour 59, 1127-113.] and thus grooming between members of the same colony (nest-mates) is frequent.
Allogrooming is found in many social insect species and is a behaviour thought to facilitate the exchange of cuticular hydrocarbons involved in recognition cues.
For many social insects that are haplodiploid (producing some offspring with higher relatedness than others), well known theory of inclusive fitness is accepted to explain social behaviour. However, since termites are homoploid (producing only diploid offspring), inclusive fitness does not always explain termite social behaviour, necessitating further study.
Read the peer reviewed article published in the Royal Society Open Science online journal in 2016, as a results of the above mentioned work…
P. occidentis Study System
In September 2011, 4 colonies of varying instar composition and size (34, 112, 139 and 170 individuals) were extracted from dead Cercidium microphyllum trees at four different nesting sites near Tucson, Arizona.
Each colony was contained inside a transparent Perspex box (206mm x 306mm x 31mm). Inside, slices of 8mm thick Cercidium microphyllum wood was packed next to each other to form an observable termitatium for each colony.
The colonies were maintained in an incubator set at 28±2°C from 09:00 to 17:00 and 18±2°C from 17:00 to 09:00, on a corresponding Light-Dark cycle, and at a constant low humidity. Water was provided in the form of droplets generously sprinkled over the wood every two weeks.
Each colony was allocated separate equipment and wood stock to control for cross-contamination of colony specific cuticular hydrocarbon compounds.
In Theory 